1. Field of the Invention
This invention relates to a recording disk drive technology applied to an information recording device wherein a disk recording medium is rotated for information exchange, and in particular to a recording disk drive and driving method thereof for an information recording device wherein a stepping motor is used for a driving source for rotating the disk recording medium.
2. Description of the Prior Art
For writing and reading information into and from a disk-type information recording media, i.e., so-called floppy disks used in word processors and personal computers, a floppy disk drive (hereinafter referred to as "FDD") is used. So far a brushless DC motor has been used as a spindle motor rotating the disk in the FDD,
The characteristics and reliability of the brushless DC motor is satisfactory as the disk drive motor. However, the necessity of a rotor position detector and a speed detector necessarily renders the motor drive circuit expensive. In other words, it leads to make the drive circuit be equipped with a rotation speed feedback control system in order to assure accuracy of rotation, and as a result the circuit construction becomes so complicated not to comply with a demand for manufacturing cost reduction. For this reason, developments of a low cost stepping motor has been studied for a spindle motor driving the recording media.
On the other hand , since the stepping motor is regarded as a permanent magnet-type synchronous motor in a broad sense, a fatal problem called "step out" is inherent in it. In particular, a rated rotation speed is often used in a pull out area of the motor in such an information recording device as to make use of a flywheel effect caused by an increased inertia of the rotating part and thereby improve accuracy of rotation, in which case said motor cannot restart forever even if disturbance of load is removed.
As a countermeasure, it is needed to adopt any circuit for restarting the motor when a step out occurs for some cause during operation.
Needless to say, phenomenon of a step out does not occur in a configuration in which a traditional brushless DC motor is used. Even if the motor stops, only removal of the disturbance of load automatically leads to its restarting. Then, a restarting circuit as mentioned above is unnecessary.
A stepping motor as described above can easily be driven with a desired rotation speed by use of a low-cost digital circuitry. However, in order to assure accuracy of its rotation speed, an inertia of a rotating part of the motor is increased. As a result, it will cause a fatal problem that the motor never restarts once a step out occurs for some cause because the rated rotation speed shifts from a pull-in area to a pull-out area of the motor.